Can I suggest Salt & Pepper Cories (corydoras habrosus), rather than Pygym Cories? As Snazy says, Pygmies are more mid-water swimmers, whereas S&Ps are bottom dwellers, and are darker, so they'll show nicely against your light substrate. They can be quite difficult to get hold of, but well worth it. I had a shoal for a while, and still have the last one.
